Online

Solomon, Laura

Cellular, Molecular, and Biomedical Sciences Graduate Program

2016

M.S.

The cover of the heart, or epicardium, consists of a single layer of mesothelial cells. During cardiac development, epicardial cells undergo Epithelial-to-Mesenchymal Transition (EMT) to form multipotent precursors known as epicardial-derived cells (EPDC). The EPDC migrate into myocardial tissue (containing cardiomyocytes) and subsequently differentiate into fibroblasts, myofibroblasts, and smooth muscle cells. In adult hearts, a similar process of epicardial cell proliferation, migration, and differentiation occurs after myocardial infarction (MI, heart attack). EPDC differentiation into vascular endothelial cells or cardiomyocytes is rare and not well understood. Recently, we observed that running (exercise) in mice promotes differentiation of EPDC into microvascular endothelial cells (CD31+). After running, EPDC appear to generate endothelial cells and not other cardiac cell types. Of interest, running promotes cardiac hypertrophy that requires additional perfusion (blood flow) and may therefore stimulate the contribution of EPDC to capillaries. We hypothesized that running exercise induces gene expression in epicardial cells that promotes endothelial specification. To test our hypothesis, we developed an efficient method to directly isolate primary adult epicardial cells from the heart cover based on their expression of integrin-[Beta]4 (CD104). After 2 hours of protease digestion, we used Magnetic-Activated Cell Sorting with antibodies against CD104 (CD104 MACS) to obtain undifferentiated epicardial cells; this was confirmed by expression of Keratin-18, an epicardial-specific protein in the heart. By cDNA microarray assays and bioinformatics analysis, we compared the gene expression profile of epicardial cells isolated from running-conditioned mice with that of age-matched controls (non-runners). Our data suggest that extracellular matrix remodeling in the heart is mediated, in part, by epicardial cells during running. Furthermore, we identify epicardial gene expression for cell signals/pathways and transcription factors that may enhance vascular perfusion after MI through promoting angiogenesis or endothelial specification of epicardial derivatives.